Thursday, December 11, 2008

The Milky Way

The Milky Way (Latin: Via Lactea) is a barred spiral galaxy; a gravitationally bound collection of roughly two hundred billion stars. As part of the Local Group of galaxies, the Milky Way is one of billions of galaxies in the observable universe and is the home galaxy of our Solar System. The plane of the Milky Way galaxy is visible from Earth as a band of light in the night sky, and it is the appearance of this band of light which has inspired the name for our galaxy. Our Sun is one of these stars and is located roughly 24,000 light years (or 8000 parsecs) from the center of our the Milky Way.

The Milky Way, along with Andromeda Galaxy, is the most massive member of the the Local Group and has a system of satellite galaxies. Viewed from the Earth, the Milky Way galaxy appears in the night sky as a hazy band of white light which originates from stars and other material that lie within the galactic plane. The center of the galaxy is in the direction of Sagittarius. The stellar disk of the Milky Way galaxy is approximately 100,000 light-years in diameter, and is believed to be, on average, about 1,000 ly (9.5×1015 km) thick and is estimated to contain at least 200 billion stars.

The age of the Milky Way is estimated to be about 13.2 billion years, nearly as old as the universe itself. This estimate is based on research by a team of astronomers in 2004 using the UV-Visual Echelle Spectrograph of the Very Large Telescope to measure, for the first time, the beryllium content of two stars in globular cluster NGC 6397.